Hint:<?phpin_array("your-interface", class_implements($object_or_class_name));?>would check if 'your-interface' is ONE of the implemented interfaces.Note that you can use something similar to be sure the class only implements that, (whyever you would want that?)<?phparray("your-interface") == class_implements($object_or_class_name);?>

I use the first technique to check if a module has the correct interface implemented, or else it throws an exception.